1. Scope of the Invention
This invention relates to a process for the production of diethoxymethane. More particularly it relates to an improved process for the reaction of formaldehyde and ethanol in the presence of an acidic catalyst to form diethoxymethane in high yields without the need for auxiliary drying agents, and with shorter reaction times. As described in detail below, this is achieved by the recovery of the product by azeotropic distillation of the product with one of the reactants, followed by a second azeotropic distillation to recover substantially pure product.
2. Description of the Prior Art
Diethoxymethane, also known as ethylal, is a valuable intermediate used in agricultural chemicals manufacture and the perfume industry. A few literature preparations of diethoxymethane are known but are unsuitable for large scale industrial production. Two known procedures for preparing diethoxymethane [J. N. Zaganiaris, Chem. Ber., 71, 2002 (1983); N. I. Shulkin and N. A. Pozdnyak, Sbornik Statei Obschchei Khim., 2, 1014 (1953)] involve the acid-catalyzed equilibrium controlled reaction of formaldehyde with ethanol (1). ##STR1## In both of these literature cases, a large amount of drying agent is employed to remove the water, thereby achieving higher conversion of formaldehyde. When auxiliary chemicals are used in such excess, however, they result in homogeneous solutions, making it difficult to design a process. This is especially true if, for economic reasons, it is necessary to recycle or regenerate the drying agents.
Another method of preparing diethoxymethane [U.S. Pat. No. 3,492,356 (1970) to D. W. Hall] is essentially the same except that a quite large amount of N-methylacetamide is added to the reaction. This procedure is intended primarily for use in preparing methylal; it has not been established that it also works for diethoxymethane.
Arundale, U.S. Pat. No. 2,421,862, teaches making and recovering cyclic acetals generally, and in that context mentions that ethanol and ethylal form an azeotrope. No suggestion of the use of this fact in the preparation and recovery of diethoxymethane in high purity when combined with other steps is made; however, Guinot, U.S. Pat. No. 1,850,836, teaches an analogous process whereby a solvent is added to an acetal to form an azeotrope. Again, however, the application of this step to a different, multistep, high purity recovery method of diethoxymethane is absent from this teaching. Finally, Michael, U.S. Pat. No. 2,617,757, teaches the well-known fact that certain solvents form azeotropes with ethanol, but fails to suggest how this can be applied to the high purity preparation and recovery of diethoxymethane.
There are three main difficulties in preparing diethoxymethane from formaldehyde and ethanol. One problem is that the equilibrium does not favor the formation of the product. A second problem, associated with the first, is that the reaction is slow to reach equilibrium when using most known soluble and insoluble acid catalysts. Finally, assuming less than complete conversion of ethanol, it is difficult to separate the diethoxymethane from the azeotropes it forms with both ethanol and water. Thus, it is an object of this invention to overcome each of the foregoing disadvantages, and to provide a more economical process for the production of diethoxymethane.